By way of example, U.S. Pat. No. 3,985,194 has disclosed a hydraulic cab-tilting device. This known device has a pair of double-acting tilting cylinders, each having a first and a second connection. Furthermore, there is a pump having one single pumping direction, which pump has a suction port which is in communication with a reservoir for hydraulic fluid and a single delivery port for delivering pressurized hydraulic fluid to the tilting cylinder(s). A manually actuated valve, the inlet passage of which is connected to the delivery port of the pump, is provided for retracting or extending the piston rods of the tilting cylinders as desired, which valve has a shut-off member, so that in a first position thereof the delivery port is connected to the first connection of the tilting cylinder and in the second position thereof the delivery port is connected to the second connection of the tilting cylinder.
Cab-tilting systems are also known in which the pump is of the type having two pumping directions, i.e. having two pump ports which act as a suction port or delivery port depending on the direction of rotation of the generally electric drive motor. The pump ports are each directly connected, via a line, to the connections of the cylinder. Rotating the drive motor in one direction then, for example, causes the piston rod of the cylinder to be retracted, and when the drive motor is rotating in the other direction the piston rod slides outwards. The direction of rotation of the pump in this case therefore functions as a control parameter.
One drawback of a pump with two pumping directions compared to a pump with a single pumping direction is that the pumping efficiency of a two-direction pump is often lower, and two-direction pumps are often also more expensive. This is offset by the fact that the additional control valve which is required in a pump having a single pumping direction represents additional costs and requires an additional feature for activating this control valve.